Roots-type gear compressors are well known in the prior art, and have existed in various configurations for many years.
Such Roots style gear compressors typically comprise a pair of intermeshing rotors placed side by each so as to permit meshing of lobes on each of said rotors, for the purpose of transferring quantities of compressible fluid from a low pressure region to a high pressure region.
In early non-helix type gear compressors having lobed rotors, it was realized that at high circumferential velocities of the gear rotors in the range of 1/10 the speed of sound, adverse momentum loses become significant. These losses occur as a result of the sudden exposure of the gear wells between the gear lobes which are filled with low pressure inlet gas to the high pressure outlet region, bringing about a violent rush of high pressure gas back against the oncoming gear lobe thereby creating adverse momentum forces which impede the rotor's rotation and thereby require greater horsepower to operate.
Accordingly, in one improvement related to non-helix gear type compressors, as shown in U.S. Pat. No. 3,531,227 to Weatherston, a plurality of feedback passages were provided (by drilling or coring) extending from the discharge plenum through the sides of the cylindrical chambers containing such gears, which permitted high pressure discharge gas to then impact on a rear face of each lobe so as to allow a reaction force thereon which acts in the direction of motion of the gears and therefore functions to augment the work imparted to the gears, thereby reducing the horsepower requirement required to drive the compressor.
U.S. Pat. No. 4,215,977 also to Weatherston discloses a similar concept for providing a three-lobe (now-helix) type Roots blower with feed back structure within the sides of the cylindrical chambers containing such rotors, to bring the gas trapped in the rotor well up to the discharge pressure prior to delivery. Specifically machined surface was provided over an angular portion φ of each of the cylindrical chambers which allowed high pressure discharge air to enter trapped wells during a rotation of the rotors to reduce discharge pulses.
Disadvantageously, in the case of the gear compressor disclosed in U.S. Pat. No. 3,531,227 the provision of a plurality of feedback passages in the sides of the chamber was an expensive machining or casting step, requiring extensive and complicated machining or creating of expensive molds, making such feature undesirably expensive.
Likewise disadvantageously in the case of the (non-helix) Roots blower disclosed in U.S. Pat. No. 4,215,977, the machined surface provided a loss of seal for a portion of the rotation of each rotor, thereby having an offsetting efficiency loss.
Roots-type superchargers or “blowers” having helical rotors have been used, such as of the type shown in U.S. Pat. No. 2,014,932, which provide for two 3-lobed rotors with an approximate 60° helical twist for the lobe on each of such two rotors, to more uniformly dispense pressurized air thereby reducing cyclical pulsing each time a trapped volume rotates into contact with the high pressure discharge air of the discharge port.
U.S. Pat. No. 4,556,373 to Soeters, Jr. teaches an improved supercharger or blower, having a pair of 3-lobed rotors, each with an approximate 60 helical twist. As shown in FIG. 9 and FIG. 16 thereof, pairs of recesses 46 and 48 in a front end wall 20 (see FIGS. 9 and 15) and pairs of recesses 58, 60 in an end wall are provided, which are variably covered and uncovered at times by the lobes of the rotors.
U.S. Pat. No. 2,578,196 to Montelius, discussed in U.S. Pat. No. 4,556,373 to Soeters, Jr. above, teaches a screw type compressor having a pair of non-uniform but meshably engageable rotors, with one end of one of the cooperating rotors being closed by a valve plate, which in the valve plate passages from each rotor groove are made adjacent to one side of the rotor threads and cooperate with a channel in the end wall, which is connected to the outlet but covered by a valve plate. The channel drains trapped volumes when exposed by said valve plate directly to the compressor discharge outlet.
More recently, superchargers having rotors with helically arranged lobes such as those manufactured by Kobelco Compressors (America) Inc. have become publicly available. These are of the “backflow” type, where air is drawn in at a location proximate the front end thereof and proximate the top of the blower, and which by rotating helixes on each of the rotors, is drawn downwardly and axially rearwardly, wherein upon reaching the opposite end of the blower, is forced backwards via said helical lobes on said rotors and forcefully expelled from a high pressure discharge port on the bottom side of the blower towards the front end of such compressor.
A need exists for modifying such Kobelco superchargers for increased efficiency so as to require less horsepower for providing the same volume and pressure of compressed air or compressible fluid.